1. Field of the Invention
The present invention relates to a carbon coated aluminum foil as a cathode of solid aluminum electrolytic capacitors and a manufacturing method thereof, especially to a carbon coated aluminum foil as a cathode of solid aluminum electrolytic capacitors with good mechanical strength, high conductivity, high capacitance ratio, high power density and long use life and a manufacturing method thereof.
2. Description of Related Art
Capacitors are used for charge storage, blocking direct current, allowing alternating current to pass in filters, tuning and oscillation. Different capacitors have different features so that their functions and applications are different. Among the capacitors, due to higher electrostatic capacity and lower manufacturing cost, aluminum electrolytic capacitors are applied most broadly to telecommunication products and electronic products such as power supplies, motherboard, etc.
Generally, each aluminum electrolytic capacitor includes two electrodes, anode and cathode. The anode is made of metals such as aluminum, Tantalum, etc. on which an insulating oxide film is grown. As to the cathode, it's electrolyte with an aluminum foil having large surface and used as a cathode terminal so as to increase electrostatic capacitance of the capacitor. Moreover, the volume o the capacitor is minimized along with more compact size of the appliances. Thus the aluminum foil is much thinner and the mechanical strength of the aluminum foil in the capacitor is dramatically reduced. Therefore, the service life of the capacitor is further decreased.
Some people in the business have tried to coat a carbon layer on a surface of the aluminum foil so as to increase the strength of the aluminum foil. Refer to Taiwanese Pat. No I333221 “cathode foil for capacitor and method for manufacturing the same”, aluminum foils are set in a space filled with hydrocarbons. A material containing carbon in slurry, liquid or solid state is produced by mixing carbon with binders, solvents or water. Then the material containing carbon is attached to the surface of the aluminum foils by coating or hot pressing and a carbon layer is formed on the surface of the aluminum foils.
Although the above Taiwanese patent can coat the material containing carbon on the surface of the aluminum foil, the carbon layer and the aluminum foil are connected only by binders or solvents. The carbon layer is easily falling away from the aluminum foil due to unstable connection between the carbon layer and the aluminum foil. Moreover, the binders/solvents reduce conductivity of the material containing carbon so that the electrical conductivity of the aluminum foil with the carbon layer is significantly reduced. This has negative effects on electrical conductivity, capacitance ratio, power density and use life of capacitors.
Furthermore, other patents such as Taiwanese Pub. App. No. 200423459 “aluminum coated with carbon and manufacturing method of the same”, Taiwanese Pub. App. No. 200912038 “aluminum coated with carbon and manufacturing method of the same”, and Taiwanese Pub. App. No. 201033405 “aluminum coated with carbon and manufacturing method of the same”, all reveal aluminum coated with a carbon layer and related methods. These patents have shortcomings of poor conductivity, bad capacitance ratio, poor power density of capacitors resulted from poor adhesion between the carbon layer and the aluminum, complicated manufacturing processes, and high production cost. This is not cost effective.
Thus there is a need to develop a new structure of the carbon coated aluminum foil and a manufacturing method thereof that overcomes the above shortcomings.